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Abstract: We present here the hybrid DFT level study of a series of dipeptide at 6-31g∗ basis. A rigorous computation has been performed on a series of dipeptide (keeping valine as a fixed component in the N-terminus and the component in the C-terminus are varied with eight different combinations) to investigate various geometrical parameters to understand the effect of amino acid sequence in the dipeptides. Bond lengths, bond angles have been reported. Geometry around α-carbon atom is discussed. The analysis of dihedral angles shows deviations from planarity. This has been explained in terms of the cumulative effect of steric hindrance of –R group and H-bonding. To get an idea about its conformational stability, a rigid potential energy scan has also been performed on valine by rotating –COOH and –CH(CH3)2 groups separately. [Copyright &y& Elsevier]

Abstract: Potential energy surfaces (PES) for the ground and excited state intramolecular proton transfer (ESIPT) processes in 5-hydroxy-flavone (5HF) were studied using DFT-B3LYP/6-31G(d) and TD-DFT/6-31G(d) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer (GSIPT) in 5HF. Excited states PES calculations support the existence of ESIPT process in 5HF. ESIPT in 5HF has been explained in terms of HOMO, LUMO electron density of the enol and keto tautomer of 5HF. PES scan by phenyl group rotation suggests that the twisted form, i.e., phenyl group rotated by 18.7° out of benzo-γ-pyrone ring plane is the most stable conformer of 5HF. [Copyright &y& Elsevier]

Abstract: DFT calculations has been done applying 6-31G∗ basis set on a series of dipeptides where the N-terminus position is fixed with phenylalanine and the C-terminus is varied with eight different amino acids. Different geometrical parameters (bond angle, bond length, geometry around α-carbon atom) are thoroughly investigated to study the effect of amino acid sequence on dipeptide. Dihedral angle data analysis shows the deviation of amide plane from planarity, which is due to the combined effect of the steric hindrance of –R group and hydrogen bonding. The λ max value for phenylalanine has been calculated, which shows good agreement with the experimental value. A rigid potential energy scan is performed on phenylalanine by rotating –CH2Ph, –COOH and –NH2 groups separately to get some idea about the conformational stability. [Copyright &y& Elsevier]

Abstract: Potential energy (PE) curves for the intramolecular proton transfer in the ground (GSIPT) and excited (ESIPT) states of 1-hydroxy-2-naphthaldehyde (1H2NA) and 2-hydroxy-3-naphthaldehyde (2H3NA) were studied using DFT/B3LYP(6-31G) and TD-DFT/B3LYP(6-31G) level of theory, respectively. Our calculations suggest the non-viability of ground state intramolecular proton transfer for both the compounds. Excited states PE calculations support the ESIPT process to both 1H2NA and 2H3NA. The wide difference in ESIPT emission process of 1H2NA and 2H3NA have been explained in terms of HOMO and LUMO electron density of the enol and keto tautomer of these two compounds. [Copyright &y& Elsevier]